Patent Application
20240413593
The present invention relates to dielectric modified tunable hot melt adhesive material which enables better matching between electrical components. In particular, the invention is directed to a connector which includes hot melt adhesive material with tunable hot melt adhesive composite which is tuned to have a lower dielectric constant.
With the recent rapid increase in the speed and amount of data transmission, reductions in size and weight and increases in the speed of electronic devices is often required. For such devices, electrical insulating materials with targeted dielectric constants that can accommodate high speed connector designs are beneficial. However, current compositions used to interconnect different electrical components are currently not able to provide targeted or tunable dielectric constants to better match the dielectric contact of the components. Thus, there is a need for a simple hot melt adhesive which can be tunable to a desired dielectric constant to enable better impedance matching between electrical components.
An embodiment is directed to an electrical connector assembly having a printed circuit board, signal wires, and an impedance mold. The signal wires transmit signals at a determined signal speed. The signal wires have ends which are connected to the printed circuit board. The impedance mold cooperates with the printed circuit and the signal wires. The impedance mold is formed from a tunable hot melt adhesive composition. A dielectric constant of the tunable hot melt adhesive composition is tuned to have a lower dielectric constant than the dielectric of the original base material to be compatible with the desired signal performance characteristics of the signals transmitted over the signal wires to the printed circuit board.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.
The description of illustrative embodiments according to principles of the present invention is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. In the description of embodiments of the invention disclosed herein, any reference to direction or orientation is merely intended for convenience of description and is not intended in any way to limit the scope of the present invention. Relative terms such as “lower,” “upper,” “horizontal,” “vertical,” “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivative thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description only and do not require that the apparatus be constructed or operated in a particular orientation unless explicitly indicated as such. Terms such as “attached,” “affixed,” “connected,” “coupled,” “interconnected,” and similar refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise.
Moreover, the features and benefits of the invention are illustrated by reference to the preferred embodiments. Accordingly, the invention expressly should not be limited to such embodiments illustrating some possible non- limiting combination of features that may exist alone or in other combinations of features, the scope of the invention being defined by the claims appended hereto.
As shown in
A pull tab 16 extends from the back of the housing shells 12, 14. The pull tab 16 is molded from rubber or other material having the desired characteristics. The pull tab 16 has cover mounting legs 18 which are cooperate with one or more of the housing shells 12, 14 to retain the pull tab 16 in engagement with the housing shells 12, 14 and the connector assembly 10.
Ends of wires 20 are provided in the connector assembly 10 between the housing shells 12, 14. The wires extend through a back surface 22 of the connector assembly 10. A wire positioning housing 24 is provided at the back surface 22 of the connector assembly 10 to properly position and secure the wires 20 in the connector assembly 10. Strain relief members 26 are also positioned proximate the back surface 22 to prevent the transfer of stresses applied to the wires 20 from being transferred into the connector assembly 10. Strain relief securing members 28 facilitate the positioning and operation of the strain relief members 26.
As shown in
The circuit board 32 has signal receiving pads 40, ground planes 42, ground rake receiving through holes 44 (
The immobilization mold 36 is made from a base hot melt composition or other type of material which is molded over the ends of the wires 20 to retain the wires 20 in position. The immobilization mold 36 encapsulates a portion of the circuit board 32, as shown in
In the illustrative embodiment shown, the strain relief mold 38 is positioned adjacent the immobilization mold 36 and is molded over the ends of the wires 20. The strain relief mold 38 is molded from plastic or other materials which have the strength characteristics desired. Stabilization projections 48 extend from a surface of the strain relief mold 38. The stabilization projections 48 cooperate with one or more of the housing shells 12, 14 to secure and retain the strain relief mold 38 and the internal assembly 30 in proper position in the connector assembly 10.
The wires 20 have exposed ends 50 which are mounted to the signal receiving pads 40 of the circuit board 32. In the illustrative embodiment shown, each wire 20 has a differential pair of signal conductors which are mounted to the signal receiving pads 40, as shown in
With the ends 50 properly mounted to the signal receiving pads 40 of the circuit board 32, ground members or rakes 54 are positioned over the portions of the insulated wires 20 and over the bent portions 52 of the ends 50 of the wires 20. The ground members or rakes 54 are mounted and secured to the ground rake receiving through holes 44 by means of solder or other known mounting methods.
In the illustrative embodiment shown, the impedance mold 34 is positioned adjacent the immobilization mold 36. With the ground members or rakes 54 properly mounted, the impedance mold 34 is molded over and flows between the ground rakes 54 and the bent portions 52 of the ends 50 of the wires 20. The impedance mold 34 encapsulates the ground rakes 54 and the bent portions 52 of the ends 50 of the wires 20.
The impedance mold 34 is made from a tunable hot melt adhesive composition which enables better matching of the electrical properties between the wires 20 and the printed circuit board 32. The electrical properties include, but are not limited to, necessary signal performance characteristics, including but not limited to impedance, propagation delay and crosstalk targets transmitted over and near the differential pair of signal conductors which are mounted to the signal receiving pads 40.
The tunable hot melt adhesive composition provides a hot melt adhesive composition in which the properties can be varied to achieve the desired result. In this particular instance, the tunable hot melt adhesive composition is tuned to have a lower dielectric constant than the original dielectric constant of the hot melt adhesive. The tunable hot melt adhesive composition can be formed from a thermoplastic or thermoset polymer. The tunable hot melt adhesive composition should have suitable rheological behavior in which the adhesive flow can be controlled for connector application while still maintaining the desired electrical properties without degradation of the material. In one embodiment, the tunable hot melt adhesive can be processed in the temperature range of about 190° to about 210° C. In yet another embodiment, the tunable hot melt can be processed at a temperature below 230° C.
Preferably using the instant invention, the dielectric constant of the tunable hot melt adhesive composition can be modified or adjusted from its neat composition to obtain the desired dielectric constant in the final composition. In one embodiment, the dielectric constant of the tunable hot melt adhesive is lowered from its original dielectric constant.
In another embodiment, the composition of this tunable hot melt adhesive composition is tuned to achieve a lower dielectric constant in the range of about 1.6 to about 2.5. The composition comprises a polymer and a filler, as well as possibly other additives.
The polymer of the tunable hot melt adhesive composition can be either a thermoplastic polymer or a thermoset polymer. The polymer which is used in the tunable hot melt adhesive composition is dependent upon the final end use application of the tunable hot melt adhesive composition. Examples of suitable thermoplastic polymers include polyamides, polyolefins, polyurethanes, and ethylene vinyl acetate.
Other examples of thermoplastic polymers that maybe used in the tunable hot melt adhesive composition include polyesters, poly (meth) acrylates, polycarbonates, polyvinyl alcohols, polynitriles, polyacetals, polyimides, polyarylketones, polyetherketones, polyhydroxyalkanoates, polycaprolactones, polysulfones, polyphenylene oxides, polyphenylene sulfides, polyacetates, liquid crystal polymers, fluoropolymers, ionomeric polymers, thermoplastic elastomers, and copolymers of any of them and combinations of any two or more of them.
Alternatively, the tunable hot melt adhesive composition can be formed from thermoset polymers so long as the desired viscosity, dielectric constant and dissipative factors of the composition are maintained. Examples of suitable thermoset polymers to be used in a tunable hot melt adhesive composition include but are not limited to epoxies, acrylates, cyanoacrylates, and reactive polyurethanes.
In addition to the polymer, the tunable hot melt adhesive composition includes fillers. The fillers that can be used in the tunable hot melt adhesive composition include but are not limited to: thermoplastic hollow spheres and hollow glass spheres or combinations thereof. The size of the filler should be selected so that the filler can be incorporated into the polymer to maintain the desired viscosity, dielectric constant and dissipation factor of the tunable hot melt adhesive composition. The filler is about 0.5% to about 35% by weight of the tunable hot melt adhesive composition. The filler induces voids in the hot melt adhesive composition. Alternatively, chemical foaming, aerogels, Mucell technology can be used to produce the same effect.
Thermoplastic hollow spheres generally contain a thermoplastic shell which encapsulates a gas. These thermoplastic hollow spheres can be pre- expanded or unexpanded prior to use. With heat, the internal pressure of the encapsulated gas increases and expands the outer thermoplastic shell. Preferably, the unexpanded thermoplastic hollow spheres are used. In one embodiment, the thermoplastic hollow spheres have a density of less than 0.014 g/ml and a particle size in the range of about 20 to about 40 microns. In one embodiment in which only thermoplastic hollow spheres were used in the tunable hot melt adhesive composition, the thermoplastic hollow spheres comprised from about 0.5 to about 3.5 weight percent of the composition. An example of a commercially available thermoplastic hollow sphere which can be used in the instant invention is Expancel® microspheres available from Nouryon Chemical Holding BV.
Alternatively, hollow glass spheres can be used as the filler to lower the dielectric constant (Dk) of the tunable hot melt adhesive composition. Hollow glass spheres generally include soda-lime borosilicate shells which encapsulate air. Preferably, the density of these hollow glass spheres ranges from about 0.15 to about 0.4 g/ml with a particle size in the range of about 30to about 60 microns. In one embodiment, the hollow glass squares comprise from about 10 weight percent to about 35 weight percent of the tunable hot melt adhesive composition. An example of a commercially available hollow glass sphere which can be used in the composition is 3M™ Glass Bubbles, available from Minnesota Mining and Manufacturing Company, St. Paul, Minnesota.
The tunable hot melt adhesive composition may include additional additives provided that the desired viscosity, dielectric constant and the dissipation factor are maintained. Examples of conventionally employed additives include pigments, dyes, voiding agents, antistatic agents, foaming agents, plasticizers, radical scavengers, anti-blocking agents, anti-dust agents, antifouling agents, surface active agents, slip aids, optical brighteners, plasticizers, viscosity modifiers, gloss improvers, dispersion stabilizers, UV stabilizers, UV absorbers, antioxidants, lubricity agents, heat stabilizers, hydrolysis stabilizers, cross-linking activators, layered silicates, radio opacifiers, such as barium sulfate, tungsten metal, non-oxide bismuth salts, fillers, colorants, reinforcing agents, adhesion mediators, impact strength modifiers, antimicrobials, and any combination thereof. Such additives may be included in conventional amounts. Preferably, these additional additives are generally in the range of about 0.5% to about 10%, by weight of the composition of the tunable hot melt adhesive. These additive can be mixed into the tunable hot melt adhesive composition in any conventional manner desired, to achieve the desired properties in the hot melt adhesive.
The density of the tunable hot melt adhesive ranges from about 0.32 to about 0.73 g/mL when thermoplastic hollow spheres are used in the composition. The density of the tunable hot melt adhesive ranges from about 0.44 to about 0.87 g/mL when glass spheres are used in the composition. The neat polymer used in the tunable hot melt adhesive has a density of about 0.98 g/mL.
The flow behavior of the tunable hot melt adhesive composition was assessed using oscillatory rheology and complex viscosity values were used to compare the tunable hot melt adhesive composition formulations to the neat polymer used in such compositions. The neat polymer viscosity is around 4.5 Pa.s. When the tunable hot melt adhesive composition is formed with the polymer and the thermoplastic hollow spheres, the complex viscosity is in the range of about 13 Pa.s to 200 Pa.s. When the tunable hot melt adhesive is formed with glass spheres, the complex viscosity ranges from about 20 Pa.s to 8×105 Pa.s.
In another aspect, the invention relates to the preparation of the tunable hot melt adhesive composition. The process comprises providing a polymer, providing at least one filler and optionally an additive. The polymer, and filler and optional additive are mixed together in particulate form using any conventional process to mix materials together. The mixing equipment can be any suitable equipment in the art of mixing concentrated solids. Examples of such suitable equipment include high speed Henschel mixers, ribbon blenders, shakers, extruders and the like. The fillers are configured to provide a polymer composition with appropriate physical properties, such as high heat resistance and high mechanical strength
Prior to application, the tunable hot melt adhesive composition is heated and applied in a molten state to form the impedance mold 34. The viscosity and particle size of the tunable hot melt adhesive composition are optimized to provide the desired electrical characteristics, as previously discussed, and to appropriate flow characteristics to allow the tunable hot melt adhesive composition to properly fill all of the voids between the ground rakes 52, the ends 50 of the wires 20 (including the bent portions 52), the signal receiving pads 40 of the circuit board 32 and the ground planes 42 of the circuit board 32.
The temperature and the force of application of the tunable hot melt adhesive composition onto the wires 20 and the printed circuit board 32 must also be controlled or tuned based on the characteristics of the wires 20 and the printed circuit board 32. The application of the tunable hot melt adhesive composition must be done a temperature which is below the melting point of the components of the wires 20. The force or pressure at which the tunable hot melt adhesive composition is applied must below the force or pressure which would cause the wires 20 to deform or compress. Any such deformation of the bent portions 52 of the ends 50 of the wires 20 could cause an unwanted change in the signal transmission of the wires 20.
The present invention is directed to tunable hot melt adhesive composition in the form of an impedance mold 34 which can be adjusted or tuned to have a lower dielectric constant which is compatible with the necessary signal performance characteristics, including but not limited to impedance, propagation delay and crosstalk targets transmitted over and near the connection between the ends 50 of the wires 20 and the circuit board 32. The tunable hot melt adhesive composition in the form of an impedance mold 34 is tuned to be between the impendence of the ends 50 of the wires 20 and the impedance of the circuit board 32, thereby bridging the impedance difference between the components to allow better and more even flow of current from the ends 50 of the wires 20, across the impedance mold 34, and to the printed circuit board 32.
By altering the composition of the tunable hot melt adhesive composition in the form of an impedance mold 34 the dielectric characteristics of the impedance mold 34 and the connector assembly 10 can be tuned to minimize propagation delay of the signals as the signals are transmitted over the signal wires to the circuit board, thereby minimizing interference to the signal transmitted based on the signal speed, which in turn optimizes the signal transmission.
One skilled in the art will appreciate that the invention may be used with many modifications of structure, arrangement, proportions, sizes, materials and components and otherwise used in the practice of the invention, which are particularly adapted to specific environments and operative requirements without departing from the principles of the present invention. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being defined by the appended claims, and not limited to the foregoing description or embodiments.
